Monitoring PET quality in real time while processing
By Barry Copping
Posted 3 July 2012
Aurora, Illinois-based Processing Technologies International (PTi), a manufacturer of sheet extrusion machinery, has launched a real-time intrinsic viscosity (IV) monitoring system designed to deliver better quality assurance and potentially lower costs for PET sheet production.
The system, developed in cooperation with Plastic Technologies of Holland, Ohio, allows for the material formulation (whether recycled, virgin, or post-consumer) to be adjusted online with a view to maximising product performance.
Intrinsic viscosity is a measure of the molecular weight distribution of PET. The performance of the material (in terms of impact resistance, clarity, and strength) is greater the higher the IV value.
The real-time monitoring system is an invaluable process tool, says PTi, because it identifies process deviations online so that they can be corrected to maintain consistent and efficient production. The company cites the example of formulations containing both virgin and recycled materials (whether industrial scrap or post-consumer recyclate) which can be adjusted and optimally balanced to maximise performance. More virgin PET can be added if the IV value is off-specification, and more recycled material can be added if the IV value is unnecessarily high.
James Johnson, PTi’s senior vice president for applications and technology says “Instantaneous IV measurement can provide quality assurance for an entire batch of PET sheet, ensuring that material with an off-specification IV value will no longer be discovered during forming.”
The IV monitoring system works from precise measurements of melt temperature and capillary piping pressures. These results are benchmarked against the ASTM D4603-86 standard test method for measuring IV. An accuracy of ±0.02 decalitres per gramme is claimed. The data are fully integrated into PTi’s Titan Plus control system for both real-time and historical trending analysis. The new system offers distinct advantages over offline solution test methods, according to PTi, since these are time-consuming and slow to deliver results.
PTi is initially targeting twin-screw PET sheet extrusion systems, but the monitoring system is also applicable to single-screw systems.
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